A multi-degree-of-freedom quasi-zero-stiffness air spring active vibration isolation device

Abstract

A multi-degree-of-freedom quasi-zero stiffness air-floating spring active vibration isolation device is provided to solve the problem of how to effectively isolate vibrations during ultra-precision machining. The present invention includes an upper isolator plate, a lower isolator plate, an isolator air cavity, an active vibration reduction unit, and the isolator air cavity is installed between the upper isolator plate and the lower isolator plate. An active vibration reduction unit is provided on one side of the isolator air cavity. The present invention ensures low vertical stiffness and quasi-zero horizontal stiffness. The vertical stiffness can also be reduced by an external air chamber. The active vibration reduction unit mainly includes a horizontal motor and a vertical motor, which can realize active control in two directions. Three or more such vibration isolation devices can also be assembled into a six-degree-of-freedom zero-stiffness active vibration isolation system. Taking into account the advantages of large load capacity, extremely low stiffness, and high vibration isolation efficiency, it can meet the vibration isolation requirements of the photolithography system. The present invention belongs to the field of precision instrument vibration isolation control technology.

Description

Technical Field

[0001] The present invention relates to a vibration isolation device for a photolithography machine, in particular to a multi-degree-of-freedom quasi-zero-stiffness air floating spring active vibration isolation device. The present invention belongs to the technical field of precision instrument vibration isolation. Background Art

[0002] With the development of cutting-edge scientific research fields such as precision manufacturing and processing, precision optoelectronics, and aerospace technology, researchers and institutions are increasingly demanding stricter requirements for system structural stability and measurement accuracy. A key factor limiting improvements in structural stability and system accuracy is the impact of vibration interference, particularly low-frequency, minute vibrations. These micro-vibrations have become a bottleneck for many cutting-edge technological applications. High-performance vibration isolation technology addresses this micro-vibration problem by isolating ambient micro-vibrations, providing an ultra-stable operating environment for precision equipment.

[0003] Vibration reduction theory shows that passive vibration isolation systems reduce vibration when the frequency of external interference is greater than 1.414 times the natural frequency of the isolation system. While they can effectively isolate medium- and high-frequency vibrations, they are less effective at isolating low-frequency vibrations, especially ultra-low-frequency vibrations. To improve the passive vibration isolation system's ability to isolate low-frequency vibrations, it is necessary to lower the system's natural frequency. Reducing the system's stiffness can directly reduce the system's natural frequency, but lower system stiffness often means a decrease in load capacity. Therefore, finding a way to maintain load capacity while reducing system stiffness is a hot research topic. Furthermore, active control can effectively improve the low-frequency isolation efficiency of passive vibration isolation systems.

[0004] During ultra-precision machining, environmental micro-vibrations have a significant impact on machining accuracy and surface quality. Whether or not vibrations can be effectively isolated has become a key technical issue in improving the manufacturing technology level of large-scale, high-end, ultra-precision instruments and equipment. Taking the extreme ultraviolet lithography machine, a cutting-edge machining equipment, as an example, its machining needs to meet the production of nano-scale process chips. The core components of the lithography machine, such as the laser interferometer and projection objective lens, are significantly affected by micro-vibration noise. External wide-band and micro- and ultra-micro-amplitude vibrations can easily cause vibrations in sensitive components through the supporting structure. This vibration is a key obstacle to the accuracy of ultra-precision manufacturing equipment and seriously affects the machining quality of the lithography machine. Therefore, the development of high-performance micro-vibration isolation systems to control micro-vibration noise has become the key to ensuring the accuracy and stability of ultra-precision machining and experimental equipment. Summary of the Invention

[0005] The present invention aims to solve the problem of how to effectively isolate vibration during ultra-precision machining to improve the machining quality of a photolithography machine, and further proposes a multi-degree-of-freedom quasi-zero stiffness air floating spring active vibration isolation device.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] The invention comprises an upper vibration isolator plate, a lower vibration isolator plate, an air cavity of the vibration isolator, an active vibration reduction unit and the air cavity of the vibration isolator is installed between the upper vibration isolator plate and the lower vibration isolator plate, and an active vibration reduction unit is arranged on one side of the air cavity of the vibration isolator.

[0008] Furthermore, the vibration isolator air cavity includes an inner cylinder, an outer cylinder, a rubber hinge and an inner cylinder ring belt. The inner cylinder and the outer cylinder are arranged from inside to outside. The lower surface of the upper plate of the vibration isolator is connected to the upper end of the inner cylinder of the vibration isolator through a rubber hinge. An inner cylinder ring belt is provided between the inner cylinder and the outer cylinder of the vibration isolator.

[0009] Furthermore, an outer cylinder air hole is provided at the lower portion of the outer cylinder of the vibration isolator.

[0010] Furthermore, an upper ejector pin and a lower ejector pin are provided at the upper end of the inner cylinder of the vibration isolator, and a rubber hinge is located between the upper ejector pin and the lower ejector pin.

[0011] Furthermore, a multi-degree-of-freedom quasi-zero stiffness air floating spring active vibration isolator also includes a limit unit, which includes three limit structures and limit piles. The limit piles are vertically installed between the upper plate and the lower plate of the vibration isolator and are located on the right side of the vibration isolator air cavity. The three limit structures are installed at three angular positions on the upper surface of the upper plate of the vibration isolator.

[0012] Furthermore, the active vibration reduction unit includes a horizontal voice coil motor, a vertical voice coil motor, a sensor bracket, a motor bracket and a water-cooling manifold. The motor bracket is vertically installed between the upper plate and the lower plate of the vibration isolator and is located on the left side of the vibration isolator air cavity. The horizontal voice coil motor and the vertical voice coil motor are respectively installed on both sides of the motor bracket. The sensor bracket is vertically installed between the upper plate and the lower plate of the vibration isolator. The water-cooling manifold is installed on the upper surface of the lower plate of the vibration isolator.

[0013] Furthermore, an air inlet hole is provided on the lower plate of the vibration isolator.

[0014] The beneficial effects of the present invention are:

[0015] 1. Based on the non-contact air bearing structure, the present invention introduces active vibration reduction control based on a voice coil motor. The air bearing can provide a large load capacity, while its theoretical stiffness is close to zero.

[0016] 2. The present invention can not only isolate the influence of environmental vibration interference, but also has a significant inhibitory effect on the vibration caused by the load itself;

[0017] 3. The present invention comprehensively utilizes the advantages of the air flotation system and the voice coil motor. On the basis of gravity compensation and passive vibration reduction of the air flotation system, the voice coil motor is used for precise positioning and active vibration reduction.

[0018] 4. The present invention combines the advantages of large load capacity, extremely low stiffness and high vibration isolation efficiency, and can meet the vibration isolation requirements of the lithography system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0020] Figure 2 It is a structural diagram of the air cavity of the vibration isolator;

[0021] Figure 3 It is a structural diagram of the vertical motor coil;

[0022] Figure 4 It is a structural diagram of the horizontal motor coil. DETAILED DESCRIPTION

[0023] Specific implementation method 1: Combination Figures 1 to 2 This embodiment describes a multi-degree-of-freedom quasi-

[0024] The zero-stiffness air floating spring active vibration isolator includes an upper vibration isolator plate 1, a lower vibration isolator plate 2, an air cavity 3 and an active vibration reduction unit. The air cavity 3 is installed between the upper vibration isolator plate 1 and the lower vibration isolator plate 2. An active vibration reduction unit is provided on one side of the air cavity 3. Figure 1 shown.

[0025] like Figure 2 As shown, the vibration isolator air cavity 3 includes a vibration isolator inner cylinder 3-1, a vibration isolator outer cylinder 3-2, a rubber hinge 3-3, an inner cylinder ring belt 3-4, an upper ejector pin 3-5 and a lower ejector pin 3-6. The vibration isolator inner cylinder 3-1 and the vibration isolator outer cylinder 3-2 are arranged from the inside to the outside. The lower surface of the vibration isolator upper plate 1 is connected to the upper end of the vibration isolator inner cylinder 3-1 through the rubber hinge 3-3. An inner cylinder ring belt 3-4 is provided between the vibration isolator inner cylinder 3-1 and the vibration isolator outer cylinder 3-2. An upper ejector pin 3-5 and a lower ejector pin 3-6 are provided at the upper end of the vibration isolator inner cylinder 3-1. The rubber hinge 3-3 is located between the upper ejector pin 3-5 and the lower ejector pin 3-6.

[0026] The isolator upper plate 1, lower plate 2, and isolator air chamber 3 form the passive air flotation unit, a non-contact support structure. The upper portion of the isolator upper plate 1 is fixedly connected to the load being isolated via screws, while the lower plate 2 is fixedly connected to the foundation frame. Its primary function is to support the platform in the vertical direction and act as a passive vibration isolation system to isolate the platform from external vibrations. The air flotation unit can be roughly divided into three parts: the air chamber structure, the thrust bearing-like structure, and the radial air flotation structure. Under ideal conditions (where the air chamber pressure remains stable), these structures work together to achieve extremely low vertical stiffness and zero horizontal stiffness.

[0027] The enclosed space formed by the isolator inner cylinder 3-1 and the isolator outer cylinder 3-2 constitutes the main air chamber of the isolator air cavity 3. During operation, clean gas continuously enters the main air chamber and the external expansion air chamber through the bottom plate air inlet hole 2-1, keeping the isolator inner cylinder 3-1 suspended at the specified working height and replenishing the gas lost in the main air chamber due to static pressure flotation.

[0028] Preferably, the rubber hinge 3-3 is a cylindrical hinge with a circular cross-section, which cooperates with two ejector pins fixed on the upper plate 1 of the vibration isolator and the inner cylinder 3-1 of the vibration isolator respectively. When the main air chamber is inflated, the rubber hinge 3-3 is vertically compressed until the upper and lower ejector pins contact, so that the upper plate 1 of the vibration isolator and the inner cylinder 3-1 of the vibration isolator have great vertical rigidity when working, and the weight of the upper isolated platform is completely transferred to the air cavity structure of the vibration isolator.

[0029] Preferably, the shapes of the outer wall of the vibration isolator inner cylinder 3-1, the inner wall of the vibration isolator outer cylinder 3-2 and the main air chamber structure in the vibration isolator inner cylinder 3-1 are not limited to the attached Figure 2 The cylindrical shape shown may also be other symmetrical shapes, especially an equilateral polygonal cylinder, provided that the center of gravity and vertical principal axis of inertia of the inner and outer cylinders 3-1 and 3-2 of the vibration isolator coincide with the rotation axis of the rubber hinge 3-3.

[0030] Preferably, the lower plate 2 of the vibration isolator is provided with an air inlet 2-1;

[0031] Preferably, static pressure air flotation surfaces (typically approximately 7 μm thick) are formed between the inner wall of the isolator's outer cylinder 3-2 and the outer wall of the isolator's inner cylinder 3-1, and between the upper surface of the isolator's lower plate 2 and the lower surface of the isolator's outer cylinder 3-2 baseplate. These two static pressure air flotation structures are inflated by gas from the main air chamber through air flotation holes in the side wall of the isolator's inner cylinder 3-1 and the baseplate of the isolator's outer cylinder 3-2, respectively. Gas entering the annular air film 3-2-2 between the inner wall of the isolator's outer cylinder 3-2 and the outer wall of the isolator's inner cylinder 3-1 can be discharged to the outside through the gap between the outer wall of the isolator's outer cylinder 3-2 and the upper portion of the structure, and through the outer cylinder air holes 3-2-1 in the isolator's outer cylinder 3-2. Gas entering the bottom air film 3-2-3 between the upper surface of the isolator's lower plate 2 and the lower surface of the isolator's outer cylinder 3-2 baseplate directly overflows through the air flotation gap, forming a complete gas flow process.

[0032] The inner cylinder annular belt 3-4 is used to collect the gas emitted from the annular air film 3-2-2 and release it to the external environment through the outer cylinder air hole 3-2-1 to prevent the escaped gas from interfering with the movement of the vibration isolator inner cylinder 3-1. Its cross section is not limited to a rectangle.

[0033] Specific implementation method 2: Combination Figure 1This embodiment further includes a limiting unit comprising three limiting structures 4 and limiting stakes 5. The limiting stakes 5 are vertically mounted between the isolator upper plate 1 and the isolator lower plate 2 and located to the right of the isolator air cavity 3. The three limiting structures 4 are mounted at three angular positions on the upper surface of the isolator upper plate 1. The three limiting structures and limiting stakes are used to limit the displacement of the load platform in the six degrees of freedom directions to prevent direct friction or collision between the various isolator structures when the load platform tips over, thereby preventing damage to the isolator structure. This is especially true during commissioning, when the load platform is likely to tip over.

[0034] Specific implementation method three: Combination Figure 1 To describe this embodiment, the active vibration reduction unit of this embodiment includes a horizontal voice coil motor 6, a vertical voice coil motor 7, a sensor bracket 8, a motor bracket 9 and a water-cooled manifold 10. The motor bracket 9 is vertically installed between the upper plate 1 and the lower plate 2 of the vibration isolator and is located on the left side of the vibration isolator air cavity 3. The horizontal voice coil motor 6 and the vertical voice coil motor 7 are respectively installed on both sides of the motor bracket 9. The sensor bracket 8 is vertically installed between the upper plate 1 and the lower plate 2 of the vibration isolator. The water-cooled manifold 10 is installed on the upper surface of the lower plate 2 of the vibration isolator.

[0035] Preferably, the sensors selected are displacement sensors and speed sensors;

[0036] Preferably, the actuator is a voice coil motor. Each active vibration reduction unit uses two voice coil motors, with the vertical voice coil motor 7 providing vertical output force and the horizontal voice coil motor 6 providing horizontal output force.

[0037] Specific implementation method four: Combination Figures 3 and 4 This embodiment describes the vertical voice coil motor and the horizontal voice coil motor described in this embodiment. Both the vertical voice coil motor and the horizontal voice coil motor include a coil and a permanent magnet portion. The permanent magnet portion is a simple permanent magnet array and is not specifically described. The vertical motor coil and the horizontal motor coil portions are designed separately:

[0038] like Figure 3 As shown, the vertical motor coil includes a water-cooling quick connector 7-1, a temperature sensor connector 7-2, a coil connector 7-3, a motor coil frame 7-4, a temperature sensor 7-5, and a copper coil 7-6. The copper coil 7-6 connects to the coil connector 7-3 via a groove on the motor coil frame 7-4. The temperature sensor 7-5 communicates with the controller via the temperature sensor connector 7-2 on the outside of the motor coil frame. There are two water-cooling quick connectors 7-1, one serving as the inlet and one outlet for the cooling liquid. Water flows in one direction, regardless of direction, from the inlet to the outlet, connecting to the water cooling tank. This forms a U-shaped water cooling channel in the motor coil frame 7-4.

[0039] like Figure 4As shown, the structure and connection relationship of the horizontal motor coil are the same as those of the vertical motor coil.

[0040] Working principle:

[0041] Specifically, the annular air membrane 3-2-2 only applies radial force to the isolator's inner cylinder 3-1, constraining its horizontal movement. Vertically, the annular air membrane 3-2-2 prevents mechanical contact between the isolator's inner cylinder 3-1 and the isolator's outer cylinder 3-2, allowing the isolator's inner cylinder 3-1 to float within the isolator's outer cylinder 3-2. Without friction between the inner and outer walls of the isolator's inner cylinder 3-1 and 3-2, the system's vertical stiffness and damping characteristics are entirely determined by the main air chamber within the isolator's inner cylinder 3-1. Ideally, assuming extremely high system air replenishment efficiency, the pressure changes in the main air chamber caused by the movement of the isolator's inner cylinder 3-1 would be negligible, meaning the pressure in the main air chamber would remain constant. In this case, the buoyancy force exerted by the gas in the main air chamber on the inner cylinder 3-1 of the vibration isolator is balanced with the gravity of the load, the vertical stiffness of the system approaches zero infinitely, and the vibration interference of the ground is completely isolated and filtered out from the system.

[0042] However, this theoretical characteristic presents an unavoidable problem. While the vibration damping system prevents ground vibration from being transmitted to the platform, the platform's own vibration is no longer constrained or limited, resulting in an unstable equilibrium state. Therefore, active control of the platform's vibration is necessary. Furthermore, in actual application, the air pressure in the main air chamber cannot remain absolutely stable. When the isolator's inner cylinder 3-1 moves vertically due to vibration, the volume of the main air chamber within it continuously changes. If we assume that this change occurs instantaneously, before the system's air circuit has time to replenish gas from the outside, and the gas temperature remains unchanged, the ideal gas state equation shows that as the chamber's volume changes, the internal gas pressure also changes inversely. Therefore, the system's vertical load and support forces are no longer balanced. The resultant force acts on the platform, generating a restoring force. The system's vertical stiffness is no longer zero, and its effect can be approximated by the stiffness of the main air chamber. The stiffness of the air chamber is inversely proportional to its volume. Therefore, the stiffness of the system can be reduced by increasing the volume of the air chamber. At the same time, the active system can be used to implement an active negative stiffness algorithm to further reduce the stiffness of the system and enhance the vibration reduction performance of the system.

[0043] On the other hand, the system forms a bottom static pressure air film between the upper surface of the isolator lower plate 2 and the lower surface of the base plate of the isolator outer cylinder 3-2. This air film suspends the isolator outer cylinder 3-2 above the isolator lower plate 2, and the radial stiffness of the air film is negligible, resulting in very low radial stiffness of the system. In fact, the system's radial stiffness is primarily caused by the horizontal tilting force component generated by the rubber hinge on the isolator inner cylinder 3-1. Therefore, when the isolator outer cylinder 3-2 and the isolator inner cylinder 3-1 are near their operating positions, the system's horizontal stiffness is approximately zero. The vertical stiffness of the bottom air film 3-2-3, however, is relatively large. Since it is connected in series with the main air chamber in the system, and the main air chamber's stiffness is much smaller than that of the bottom air film 3-2-3, the system's vertical stiffness can be approximately equal to that of the main air chamber.

[0044] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A multi-degree-of-freedom quasi-zero stiffness air-floating spring active vibration isolator, comprising an upper vibration isolator plate (1), a lower vibration isolator plate (2), a vibration isolator air cavity (3), an active vibration reduction unit, and the vibration isolator air cavity (3) is installed between the upper vibration isolator plate (1) and the lower vibration isolator plate (2), and an active vibration reduction unit is provided on one side of the vibration isolator air cavity (3); characterized in that: The vibration isolator air cavity (3) comprises a vibration isolator inner cylinder (3-1), a vibration isolator outer cylinder (3-2), a rubber hinge (3-3) and an inner cylinder ring belt (3-4); the vibration isolator inner cylinder (3-1) and the vibration isolator outer cylinder (3-2) are arranged from the inside to the outside; the lower surface of the vibration isolator upper plate (1) is connected to the upper end of the vibration isolator inner cylinder (3-1) through the rubber hinge (3-3); an inner cylinder ring belt (3-4) is provided between the vibration isolator inner cylinder (3-1) and the vibration isolator outer cylinder (3-2); an upper ejector pin (3-5) and a lower ejector pin (3-6) are provided at the upper end of the vibration isolator inner cylinder (3-1); the rubber hinge (3-3) is located between the upper ejector pin (3-5) and the lower ejector pin (3-6); The active vibration reduction unit includes a horizontal voice coil motor (6), a vertical voice coil motor (7), a sensor bracket (8), a motor bracket (9) and a water-cooled splitter (10), wherein the motor bracket (9) is vertically mounted between the upper plate (1) and the lower plate (2) of the vibration isolator and is located on the left side of the vibration isolator air cavity (3), the horizontal voice coil motor (6) and the vertical voice coil motor (7) are respectively mounted on both sides of the motor bracket (9), the sensor bracket (8) is vertically mounted between the upper plate (1) and the lower plate (2) of the vibration isolator, and the water-cooled splitter (10) is mounted on the upper surface of the lower plate (2) of the vibration isolator; the vertical voice coil motor (7) includes a vertical motor coil, and the vertical motor coil includes a water-cooled splitter (10) A cooling quick connector (7-1), a temperature sensor aviation plug (7-2), a coil aviation plug (7-3), a motor coil frame (7-4), a temperature sensor (7-5) and a copper coil (7-6), wherein the copper coil (7-6) is connected to the coil aviation plug (7-3) through a groove on the motor coil frame (7-4), and the temperature sensor (7-5) communicates with the controller through the temperature sensor aviation plug (7-2) outside the motor coil frame; there are two water-cooling quick connectors (7-1), which serve as a water-cooling liquid inlet and outlet respectively, and water flows from the inlet in one direction without distinguishing the direction and is connected to the water cooling box from the outlet, thereby forming a U-shaped water cooling channel in the motor coil frame (7-4).

2. The multi-degree-of-freedom quasi-zero stiffness air spring active vibration isolator according to claim 1, characterized in that: The multi-degree-of-freedom quasi-zero stiffness air floating spring active vibration isolator further comprises a limiting unit, the limiting unit comprising three limiting structures (4) and limiting piles (5), the limiting piles (5) being vertically mounted between the vibration isolator upper plate (1) and the vibration isolator lower plate (2) and being located on the right side of the vibration isolator air cavity (3), and the three limiting structures (4) being mounted at three angular positions on the upper surface of the vibration isolator upper plate (1).

3. The multi-degree-of-freedom quasi-zero stiffness air spring active vibration isolator according to claim 1, characterized in that: An outer cylinder air hole (3-2-1) is provided at the lower portion of the vibration isolator outer cylinder (3-2).

4. The multi-degree-of-freedom quasi-zero stiffness air spring active vibration isolator according to claim 1, characterized in that: An air inlet hole (2-1) is provided on the lower plate (2) of the vibration isolator.

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